Filter and filtering method

The invention provides a filter and a filtering method, and belongs to the technical field of environmental protection. The problems that an existing filter is low in filtering precision, and filter materials are lost or hardened during backwashing are solved. The filter comprises a filter cylinder, a filtered water tank, a purified water tank and a security filter, the filter cylinder is divided into an upper area and a lower area by arranging a partition plate on the middle lower portion in the filter cylinder, a plurality of filter caps are evenly distributed on the partition plate, AFM filter materials are laid in the upper area, and an annular overflow groove is formed in the upper portion of the inner wall of the filter cylinder. A water inlet of the filter cylinder is communicated with a filtered water tank through a water inlet pipe, a water outlet of the filter cylinder is communicated with a purified water tank through a water outlet pipe, and the security filter is communicated with the annular ove